Phonometer



Aug. 30, 1927. 1,641,136

H. P. DORN PHONOMETER Filed Maron 27. 1922 2 Sheets-Sheet 1 termen Aug. 30,1927. 1,641,136

H. P. DORN PHONOMETER Filed Maron 2'?, 1922 2 Sheets-Sheet 2 Use 1h19 side fororevoluhons per mnufe.

Use this side for 78 rewlufrons permiruev -Arrne/vfx- Piantada, 3o, 1927.

" UNITED STATES HARDY .F. DOEN, Ol @MELA-ND, OHIO, .-ASSIGNOB TO THE CLEVELAND TRUST COI- PANY, OF OHIO, A CORPORATION Ol' OHIO.

PHONOHETEB.

appummn ma Ima 21, ma serial no. 547,000.

This 4invention relates to means for indicating variations from a predetermined normal speed'of rotation -or other periodic movement and it is especially intended for use in 5 connection with phonographs to indicate the speed of the record turn table, and permit it to be readily adjusted to normal s d.

I The` object of the invention is to rovide a simple, inexpensive and sensitive spliced indicating device by the use of which variations 1n speed can be indicated tov permit regulation of said speed. a

To this end I make use of the stroboscopic principle in a novel manner by taking adl5 vantageiof the pulsating character of a light made by ordinary alternating electric current, as will be explained in detail in connection with the aecompan ing dra-wings which illustrate preferred em diments o the in vention.

In the drawings, Fig. 1 is a plan v1ew of the phonograph with my invention applied thereto.

Fig. 2 is a section on the line 2-2, Fig. 1.

Fig. 3 is a fragmentary perspective view of the peripheral part of a phonograph turn table illustrating a modified form `of construction.

Fig. 4 is a face view of the spaced indieating dise shown in Figs. 1 and 2.

d Fig. 5 is an opposite face view of the said isc.

Referring in detail to the construction illustrated, 1 designates the cabinet of a phonograph, 2 the tone arm thereof ,carrying at its end the usual sound box 3. 4 is the record turn table mounted on the spindle 5 which is driven in the usual manner by any suitable motor, not shown. The speed of rotation of the motor and, therefore, of

the turn table 4, is determinedby means of a brake governor (not shown) of any suitable form, the manual adjusting lever'of which is shown at 6. At one side of the table on the cabinet is mounted an electric light bulb 7 the terminals of which are connected by leads (not shown) to an alternatin cur-V 4* and on this top surface is placed a thin disc 8 which is centrally perforated to pass over the spindle 5 and may be made of any suitable material, such as a good quality ofcardboard. This dise 8 by reason of its frictiona-l engagement with the top surface of the table turns with the latter and may be ripheral part projects beyond the record as f indicated in Figs. 1 and 2.

On this Peripheral projecting part of theV disc 8 I form on one side a uniform series of marks 8 and on the other side a uniform series of marks 8b., The marks 8 and 8b can be of various forms and colors provided they contrast strongly with the background formed by the surface of the disc. I prefer however to make the marks, as shown, 1n bar form and inblaek on a white ground, and of the same width as the intervening white spaces. The numbers and spacings of the two series of marks are determined by the following considerations:

The light emitted by an electric lamp energized by alternating current consists in reality of a series of light impulses, although due to the persistence of vision the light seems to the observer uniformally contin-l uous. yTwo such light impulses occur during each complete cycle of the current, these impulses corresponding to the positive and negative maximum current values. This variation of the intensity of the light is especially marked in the case of alternating current arc lamps. In the case of alternating current incandescent lamps the effect is less `marked but Ihave discovered that it is sufliciently marked so that if the marks (8 or 8") on the stroboscopic dise are illuminated by light from an alternating current incandescent lam-p, their images formed by the maximunr light impulses referred to persist with sufficient strength and definiteness so that if the speed of rotation of the disc is such that the travel of the disc during the interval between two consecutive light impulses equals the circular pitch distance of the series oflmarks, said marks appear to stand still when the disc is rotated. There- Afore, knowing the predetermined normal speed of rotation of the phonograph turn table and the number of current alternations per 'unit of time, it is possible'to make the size and slmcings of the marks 8, or 8b, such that the marks will appear to stand still when the phonograph table turns at normal speed. whereas if it turns faster than the normal speed the marks will appear to more or less slowly advance in the direction of rotation and, if it turns more slowly than the normal speed, the marks will appear to turn more or less slowly in the reverse direction. In the case of some makes of phonograph records the normal speed of rotation is R. P. M.. while in case of other makes the normal speed of rotation is 78 R. P. M. By normal speed of rotation I mean the speed used in making the original record and the speed, therefore which should be used in playing reproductions of the original record. In common commercial practice 60 cycle alternating currents are used for lighting purposes, and an electric lam on such a circuit gives 2 60 60=7200 light impulses 'per minute. Therefore for 80 R. P. M'. the correct number of bars or marks 8 is 7 200e-80:90. Similarly it is found that 92 bars or marks are correct for approximately 78 R. P. M. In the same manner the number of marks can be determined for alternating currents of frequencies other than 60 cycles per second.

The face of the disc 8 as shown in Fi 4 is provided with 90 marks and is there ore adapted for use on phonographs rotating normally at 80 R. P. M., while the opposite face of the disc, as shown at Fig. 5, is provided with 92 marks and is therefore adapted for use with phonographs rotating normally at 78 R. P. M.

Theoretically it should be possible to secure to a measurable degree thestroboscopic effect above described if the speed of rotatlon of the disc is such that its travel during the interval between two consecutive light impulses has a commensurable ratio with the circular pitch distance of the series of marks on the dlsc when said ratio has a value other than unity as well as when it has a value of unity. Indeed, within certain limits this effect with the ratio other than unity is noticeable when an alternating current arc light is used. For example, if the said ratio be made one to two or two to one, the rotating marks clearly appear to stand stillwhen illuminated by the alternatin current arc light. However I have found/ t at when an incandescent lamp is used the stroboscopic effect described is secured clearly only when the ratio mentioned is unity. In other words, in the case of the incandescent lamp the desired effect is secured only when the conditions are most favorable.

The use of my improved indicator in connection with phonographs will readily be understood from the foregoing description. The disc 8, rotatin with the turn table and record, when illuminated by the alternating current electric light 7 indicates instantaneously'to the observer whether the turn table is rotating at the correct speed. If the speed of rotation is the correct or normal one the marks 8, or 8", appear to stand still `Whereas if the speed of rotation is too great the marks appear to slowly advance in the direction of rotation, while if the speed is too slow the marks appear to slowly move in the opposite direction. In either case the operator needs but to adjust the governor lever 6 until the indicator marks appear to remain stationary and this brings the speed exactly to normal.

It will, of course, be understood that in commercial practice the frequency of alter nating current lines is maintained with very slight variations, in factnot' to exceed one to two per cent. The commercial alternatinglighting current therefore serves as a satisfactory standard in maintaining the phonograph speed substantially constant.

I have referred to illumination of the indicator marks b the light 7 on the phonograph cabinet ut it is to be understood that illumination of said marks by alternating current lamps any place in the room will serve the purpose and the invention is not limited to any particular location for the lamp 0r lamps.

It will be seen that the discs 8 constitute a very simple indicator adapted to be applied to any phonograph. The indicator may however be made an integral part of the phonograph, as indicated in Fig. 3. As here shown the phonograph turn table 4 is formed with a circumferential extension 4 which extends radially beyond the felt top 4" of the turn table. On the top surface of the extension 4 is placed an annular series of marks 4, 90 in number, and upon the vertical cylindrical extension 4 is placed 'an annular series of marks 4", 92 in number. Thus whether the stroboscopic marks are placed upon a separate dis or the like or upon a portion of the turn table itself, the part bearing these marks can be described as means supported by the turn table bearing an annular uniform series of marks rotatable in unison with the table, and I employ language of this latter character in the appended claims accordingly.

While I have illustrated preferred embodiments of my invention, it will be understood that there can be various modifications of these embodiments without de arting from vthe invention as defined in t e appended claims.

What I claim is:

1. In a phonograph, the combination of a turn table, means for rotating the table, a manually adjustable governor for regulating the rotation of the table to a predetermined normal speed, means supported by Said table bearing, an annular uniform series of marks rotatable in unison with the table, and an alternating current incandes cent light arranged to illuminate the said marks as the table rotates` said marks having a circular pitch distance equal to their normal speed travel with the table during the interval between two consecutive light impulses due to the alternating current.

2. In a phonograph, the combination of a turn table, means for rotating the table, a manually adjustable overnor for regulating the rotation of the txizble to a predetermined normal speed, a detachable disc bearing an annular uniform series of marks and Supported to turn in unison with the table, and an alternating current incandescent light arranged to illuminate said marks as the table turns, said marks having a circular pitch distance equal to their normal speed tra-vel with the table during the interval between two consecutive light impulses due to the 'alternating current.

3. The combination of a phonograph turn table and means supported by said table bearing, an annular uniform series of marks and having a circular pitch distance approximately equal to the travel of said marks at the normal table speed during a half-cycle ofthe commercial alternating electric lighting current.

4. As a new article of manufacture, a disc adapted to be supported on a phonograph turn table to turn in unison therewith and having an annular uniform series of marks approximately equal in number to twice the number of c cles per minute of the commercial alternating electric lighting current divided by the normal number of revolutions per minute of the phonograph turn table.-

In testimony whereof, I hereunto aix my signature.

HARRY P. DoaN. 

